Transientless modulator system for keying



Dec. 7, 1948. l F. H. SHEPARD, .1R l 2,455,616

I'RANSIENTLESS MODULATR SYSTEM FOR KEYING Filed NOV. 15, 1944 -D/\ 1. AA

vi m f y u' l' I 4 INVENTIOR; v

)WHA/cfs H. SHE/ARQ JR.

`Y @wmf Patented Dec. 7, 1948 i TS TATlE fs PATE; N 4offerti-(2.15:

Inc., New "Kork, N. Y., .a

#York eorporationof -New *ApplicationiNovember 15, 1944,5fSerialfNo. 563,568

In my `Patent lNo. 32,41'195292 AAissued April U22, l4694"?, entitled System "for l transmitting two si- \multaneous` intlligences," I have disclosed a sysltem L-Wherfebyitwolfunct-ions may be simultane` ously" 1verged intoa`-=single` signal yWave by i keying 'on-1 and o'ffat `controlledintervals, thev time on representing' one r"function, and time orf repreq'sentinganother function. Ihave further shown inithatsystem means fortransmitting the sig- -nal so produced-inyvliichiit-modulates a carrier Wave before transmission. l i i viilicnthe-carrlerilrequency is *high with -respectto the modulationfrequency, -lter circuits or tuned l circuits 'maybe `used 1 to; separate the unodulation"-voltage from lthe carrier vvoltage.` How-ever, Avvlnn the 1fearr-ier 'frequency is only slightly higher than! the modulation "frequency, `so `thatV itl is necessaryr tolstart and-stop the carrier within fractional* partsA ofthecarrier cycle, `filter l *circuits `are notl'suitable" for' eliminating transients o`fmeridlat-ion"frequencyJ from thecarrier. It is -thereforeinecessary-in'such 4cases to reportto other means to eliminate such transients. The :object of thisfinvention* isA tofprovide suchfmeans feature ofthisfinventionis' a 'modulator circuit/comprising a tube through which `anode cur- `reritmaybenut-'oirperiodically, butin the intervals-when it rlowswillibe directly proportional toian 'oscillatitmvoltage; without transient effects. fBetween f the intervals-when it `flows the -voltage i output will "beequaslito` the average value' `of the oscillation Voltage Without transient effects.` Einthe drawings, i `-`Figure l 1l isL a circuit diagram` illustrating acirfcuit' LWithwifiiich luy-invention may be practiced; 'and *Figur-e `2 tis ^a =s invention.

- AIn Figure *1, f'tube "l "and fitsassociated circuits cries ofi curves4 `illustrating the `icons`titutelthe signalgeneratorin which a signal "i0 the other tube will cut off current throughthe o totherftube. The'grlidofthat tubewillth'enbe- 'come4 more positive ythan "the 'cut off voltage '1 throughfthe `gridn'esistante 'f l2l or i I"3,'as"the=case `maybe^and'currentjutillagain now; Thetime T1 (Figure i2?) may loe-controlled by the'slze lof ifresistanceilZ :tor-'condenser lor bothorfby the rsize :dffresistance |3fror inonder-15er 5` or both :and "the `Time T2 (Figure 2.)` Amay abe controlled 1 by the :otherwpair of these elements. Thus, `the condenserst! and i5 :or `zresistances i I 2 and I3, `for example, may he @made :responsive to the two 'intelligences"andy consequently,`to produce a sig- `nal representing thetwo ifunctions. l This signal, it: may be observedis similar `to the output ofsa conventional yn'niltivibratori circuit a except :forinthe tactlthatt the frequency: or: duration of the, pulses ionsuuare'iwaves Vis variableandtheduration of 'thez intervals :between: thei pulses isP 4,also variable.

These continuously variable relationshipsiconvey lthe twolintelligences, Such" intelligenceszmay be anyvitz-.is desired` toztransmit. For example-they rmay Abe fused .to transmit 1 continuously `from an airborne i radiosonde or 4remote transmitter, in

formation regarding any'V twof independent variables `such-astemperature and humidity. The circuit might also beused for the transmission by Wire 'ori by radio of :continuous information pern staining fto the i location `of two coordinates' of i the `1perror:stylus'ofa remotewriting` equipment which "information .could be demodulated andlutilized `towposition ail-reproducing penxzor-stylus for reproductionof the horizontal-and vertical com- `ipcnentsof transmitted handwriting. This signal Vis"suppliedto-thefgrid of triode Zthrough a condenser 6. During the;positive pulse of `voltage thisl grid-is driven positive to draw grid cur- -rent-tandthecondenser .E is charged by this grid currentso .-thatfon the negative swing thegrid v of triodefl` is dropped in a negative Vdirection only 0 tothepoint at which platecurrent through this triodeiscut off. l i

,During the V.time that triode v2 is .conducting full .platecurrentthat isrwhile its grid is driven positive by thesignahits cathode is drawnpositiVe, Since thecathoclemof triodemlisconnected `tu the `cathode of triode, thecathodefof triode "isalsc drawn positive. LIt is drawn sufficiently `positive 'to `cut olf the` "110W" of plate current l y`throlightriode 3 during this interval.

FA 'carrier "frequency generator `|0 produces oscillationsras illustrated by curve A, Figure 3, Whicb'arefed"tothe grid of triode 3. `While triode "3 .is'conducting itwill act as an amplifier, causing fvoltage offthe carrierrfrequency to ap- I"peau"on the anode Hxf triode 3. When rthe grid of triode2 is 'drivenfpositive to the point `Where it'cuts dii the now of. plate `current through *triode 3`,j'the ydrop the resistor 9 in the plate icircuitof"triode"wilbezerog "Theplate il of triode 3 `would accordingly 'swing positive "and introduce an undesirable transient unless means were provided to prevent it.

Curve D of Figure 2 shows the wave which would be produced at the output of the modulator triode 2, 3 with the undesired transient present. This transient consists of a sudden and undesirable rise of the zero or neutral axis of the carrier or sub-carrier voltage wave during the intervals when the wave is not being amplied through tube 3 as is indicated in Figure 2 by the rise from point I to point 2 on curve D. This high positive D. C. component would therefore be present at the output of the terminals of Figure 1, without resistor 8, instantaneously after the cutoff of current from the tube 3 and would' persist during time T1, that is, until tube 3 again becomes conducting. Curve C of Figure 2 shows the modulated wave at the output of triodes 2 3 which is desired. v

This transient is prevented by the use of a resistance 8, whi-ch is indicated as variable for the purposes of adjustment. When triode 3 is cut off so that plate current ceases to flow through the tube, the drop through resistance 9 is prevented from fallingto zero and consequently the voltage at the anode Il of triode 3 is prevented from rising by the resistance 8 which conducts current through resistance 9, resistance 8 and triode 2. The now of current through the resistance 8 accordingly will nullify or neutralize .the transient effect which would otherwise occur; By proper adjustment of the value of this resistance the upward voltage will be made to appear as shown in curve C of Figure 2.

`If .the transient effect is not corrected the displacement of the base line, as shown in curve D of Figure 2, will be passed through the output and this undesirable transient may have ill efiects on subsequent circuits. i

In claiming a particular triode section as illustrated in the drawing as a tube I do not mean to exclude from the scope of such a claim a tube in which there may be other electrodes performing other functions; and where I refer to separate tubes it will of vcour-se be understood that this may include separate electron discharge systems in a single envelope. Therefore I do not desire to be restricted to the precise form shown, but only within the scope of theappended claims.

What is claimed is:

1. The transientles-s modulator system of keying comprising a signal generator for producing a square signal wave, an oscillation generator,

means for supplying said signal wave and the output of said oscillation generator vto a modulator, means whereby said modulator passes current of oscillation frequency only during negative half cycles of said signal wave, and means for eliminating transients in the output of said modulator during positive half cycles of said signal wave. 2. A transientless modulator system of keying comprising an amplifier, means for supplying a carrier wave to saidamplier, means for periodically interrupting the flow of said carrier current through said amplier, and means for `maintainingthe anode of said amplifier at a potential during said interruptions which is its av- 'erag'e potential between said interruptions.

3. A transientless modulator system of keying 'comprisingan electronic relay, means for supplying a carrier wave to said electronic relay,

Imeans for periodically interrupting the flow of said carrier current through said electroni-c relay, and means for maintaining the anode of said therethrough, means for maintaining the cathodes of said systems at the same potential whereby current through the second system is cut'oi when said cathodes become positive due i to a positive pulse of signal current on the grid ofthe first system, and means for maintaining the anode of the second system at a. reduced voltage when no current is flowing therethrough comprising a resistance element connected between the anodes of the two systems.

. 5. A transientless modulator system of keying comprising a tube having two elements acting as grids and two elements acting as anodes in effect constituting two electron discharge systems, a condenser,I means-forapplying positive signal pulses to the grid of the rst system through said condenser whereby said system draws grid current, an impedance element between the grid and cathode of said system whereby said grid is prevented from following the signal voltage on negative pulses of said signal voltage, an impedance element in the cathode circuit of said system whereby the now of current through said system makes said cathode become positive, a connection between the cathodes of the two systems whereby the potential of the second cathode follows the potential of the first to out oi the flow of current-through the said second system Whenvsaidcathodes become positive, a second signal wave applied to the grid of said second system, and means for reducing the positive potential at the anode of said second system when current through it is cut 01T comprising an impedance element connected kbetween the two anodes.

6. A transientless modulator system of keying comprising two electron tubes, a signal wave applied to the grid of each tube, means whereby positive pulses of signal applied to one grid cut off the now of current through the other tube, and a resistance -connected between the anodes of said tubes for preventing transient effects due to the cutting oi of current through-the second tube.

7. A transientless modulator system of keying comprising two electron tubes, a signal wave applied to the grid of each tube, means whereby positive pulses of signal applied to one grid cut 01T the now of current through the other tube, and means comprising an impedance connected between the two anodes for preventing transient effects due to the cutting oil of current through the second tube.

8. A transientless modulator system of keying comprising two electron tubes, a signal wave applied tothe grid of each tube, means whereby positive pulsesof signal applied to one grid cut off the flow of current through the other tube, and means comprising a resistance connected between the two anodes for preventing transient effects due to the. cutting ofi of current through the second tube. f

9. The method of ykeying a signal wave by means of two Vacuum tubes comprising periodi- .cally interrupting the iiow of current through one of said tubes and diverting said current through the other tube during said interruptions.

the other tube to be periodically interrupted in response to said keying signal and causing current to oW between the anodes of said tubes during said interruptions.

FRANCIS H. SHEPARD,` JR.

REFERENCES CITED The following references are of record in the le of this patent:

Number UNITED STATES PATENTS Name Date Dyson Apr. 5, 1938 Taylor Mar. 14, 1939 Kinn Jan. 7, 1941 Reeves Feb. 3, 1942 Kell e Apr. 21, 1942/ Hansell Dec. 8, 1942 Harmon Jan. 4, 1944 Nagel et al Dec. 19, 1944 

